There has thus far been known an airbag folding device, as an example of an airbag folding device for mechanically folding an airbag of three pieces type by starting a horizontal folding work upon completion of a vertical folding work of the airbag (see Patent Document 1).
According to the conventional airbag folding device, the airbag has been generally folded by a method comprising a vertical folding step and a horizontal folding step, and a speed of inflation and expansion of the airbag has been generally adjusted by this folding method.
Meanwhile, although the applicant developed an airbag which expands in orderly sequence starting from a region to be first expanded and undergoes inflation and expansion without forming a lump, the folding method is to fold manually like bellows the airbag in the longitudinal direction from the tip portion of the airbag to undergo inflation and expansion toward the rear end portion to be secured to the airbag device. Since a planar shape of the airbag as folded is doughnut-shaped (the airbag as folded is hereinafter referred to as a doughnut-shaped airbag), it is impossible to fold the doughnut-shaped airbag by the airbag folding device which has been conventionally used for folding the airbag by executing a vertical folding step and a horizontal folding step.
However, an airbag folding device for forming a doughnut-shaped airbag by folding like bellows the airbag in the longitudinal direction has not been developed so far. Patent Document 1: JP 11-129847 A.